MRI Diffusion Gradient Sequences for Eddy Current Distortion Correction
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Solution Overview
Problem
Current magnetic resonance imaging (MRI) techniques face challenges in accurately processing diffusion-weighted and non-diffusion-weighted images due to eddy current-related distortions, which can lead to errors in pixel-wise determination of apparent diffusion coefficient (ADC) values, especially when using standard Steijskal-Tanner diffusion encoding.
Innovation Solution
A method that captures both diffusion-weighted and non-diffusion-weighted scan data using similar diffusion gradients, allowing for similar eddy current distortions in both datasets, enabling direct pixel-wise comparison and calculation of ADC values without additional processing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard Steijskal-Tanner diffusion encoding is used, then diffusion-weighted images can be acquired, but eddy current-related distortions occur leading to errors in ADC value determination
Solution Approach 1:
The patent applies preliminary action by acquiring non-diffusion-weighted images with the same diffusion gradients before performing diffusion-weighted imaging. This preparatory step captures the eddy current distortions in advance, allowing them to be used as a reference for subsequent correction of the diffusion-weighted images, thereby improving ADC value accuracy.
Solution Approach 2:
The patent uses non-diffusion-weighted images as an intermediary element. These images serve as a mediator that captures the eddy current effects without the diffusion weighting, enabling the separation and subsequent correction of eddy current distortions from the diffusion-weighted images through image registration and subtraction techniques.
2Reliability
If diffusion gradients are switched for diffusion encoding, then diffusion contrast is achieved, but eddy currents are induced causing image distortions
Solution Approach 1:
The patent converts the harmful eddy current effects into a beneficial reference signal. By deliberately acquiring non-diffusion-weighted images with identical diffusion gradients, the eddy current distortions are captured and transformed into a useful reference that enables precise correction of the diffusion-weighted images, turning a previously harmful artifact into a corrective tool.
Solution Approach 2:
The method performs preliminary acquisition of non-diffusion-weighted images that contain the eddy current signatures. This advance capture of distortion patterns allows for subsequent registration and subtraction operations that remove the harmful eddy current effects from the diffusion-weighted images while preserving the diffusion contrast.
3Measurement precision
If separate acquisition of diffusion-weighted and non-diffusion-weighted images is performed, then ADC maps can be generated, but additional processing steps and time are required
Solution Approach 1:
The patent merges the acquisition of diffusion-weighted and non-diffusion-weighted images into a unified processing framework. By using the same diffusion gradients for both types of images and applying image registration followed by subtraction, the method combines multiple functions into an integrated workflow that reduces processing steps and time while maintaining ADC map accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate pixel-wise processing of diffusion-weighted and non-diffusion-weighted images, reducing distortions and allowing for the generation of ADC maps without signal loss, thereby improving diagnostic image quality.
Implementation Method 1
diffusion gradients are switched for diffusion encoding of the scan data
Implementation Method 2
eddy currents induced by switched gradients
Implementation Method 3
eddy currents induced by switched gradients
Implementation Method 4
nuclear spins align along the main magnetic field
Implementation Method 5
radio frequency excitation pulses (RF pulses) are radiated into the examination object, the nuclear spin resonances produced are measured as so-called k-space data
Data Source
AI summary
Techniques are disclosed for capturing scan data of an examination object via a magnetic resonance system. The techniques include capturing a first set of a diffusion-weighted scan data by excitation and, in an acquisition phase, acquiring a first echo signal, wherein before the acquisition phase in a diffusion preparation phase, diffusion gradients are switched for diffusion encoding of the scan data, The techniques additionally include capturing a second set of non-diffusion-weighted scan data by excitation and, in an acquisition phase, acquiring a second echo signal, wherein before the acquisition phase, in a diffusion preparation phase, the same diffusion gradients are switched as are switched for diffusion encoding of the scan data of the first set of diffusion-weighted scan data, although they have no influence on the second echo signal. Diffusion-weighted and non-diffusion-weighted scan data is thereby captured, having identical disturbances caused by eddy currents induced by switched gradients.